How to use Messages to share your screen in macOS
If you need to quickly offer help to another Mac user you know, there's no quicker way to remotely provide assistance than via Apple's own Messages. Here's how to take control of another person's Mac on their behalf, and how to allow others to do the same to your desktop. The perils of family tech support can leave you needing to quickly assist a relative or friend who may be new to Mac ownership, or can't adequately search for a solution by themselves. Support over the phone can also be problematic, and while doing the configuring yourself may be the fastest way, it isn't a great idea if...
Source: appleinsider.com